There are many applications for patterned conductive surfaces. Two well known examples are printed circuit boards as used in the electronics industry, and patterned aluminum films on polyester sheet, as often used in the food packaging industry. In these and other similar applications, there is a well known manufacturing technique for mass producing the desired pattern. This technique begins with a layer of metal which is bonded to a sheet of substrate material. A resist material is deposited onto the electrically conductive metal surface by some means, in the same patterned locations as it is desired to have metal in the final pattern. The sheet is then immersed in a suitable etchant solution which has the property that it dissolves the exposed conductive surface off of the substrate, but does not dissolve the substrate, and also does not dissolve the resist material or penetrate the resist material to dissolve the metal underlying the resist material. Finally, if desired, a different etchant can be used to dissolve the resist material, leaving behind the final desired pattern in the metal layer.
A number of different methods can be used to produce the desired resist pattern, but all suffer from several disadvantages. One problem is that the production of the pattern on the resist material constitutes a completely different process from the subsequent removal of the undesired metal. Further disadvantages include the fact that many of the more economical means of producing a resist pattern, such as conventional silk screen, lithographic, or rotogravure printing techniques, involve substantial initial cost for producing a given pattern, and are therefore economical only in large quantity production of a given individual pattern. Other printing techniques, such as optical exposure of photoresist, or computer controlled ink jet printing, suffer from high equipment cost, mechanical complexity, slow processing speed, or a combination of these difficulties.
U.S. Pat. No. 4,517,045 issued May 14, 1985 for an invention of Donald E. Beckett entitled "Apparatus for Formation of Packaging Material" teaches, in an automated system, a means of producing patterns in thin film aluminum on polyester substrates. This is an example of the aforementioned economical resist production technique having high initial cost for preparing a specific resist pattern.
U.S. Pat. No. 4,767,489 issued Aug. 30, 1988 for an invention of Frederick H. Lindner entitled "Computer Aided Printer - Etcher" provides an example of an automated system for producing a desired pattern in copper layers on printed circuit boards. This patent is exemplary of a low cost technique for preparing a specific resist pattern, but having slow production rate and high equipment cost.
The foregoing examples of producing patterned conductive surfaces suffer from the cost and complexities of requiring the introduction of a resist material prior to chemical etching. The present invention provides an apparatus having an array of etching electrodes which directly produce the desired pattern on a conductive surface, without the use of a chemical resist, and therefore without the need to remove the chemical resist after etching has taken place.
Some prior art electro-chemical etching and electro-chemical machining processes use electrodes to directly etch patterns on metal-bearing substrates. This does not require a chemical resist, and therefore does not require post-etching removal of such resist. However, unlike the present invention, these prior art processes typically involve the etching of material which remains stationary relative to the electrodes, rather than undergoing continuous motion while etching occurs. If the material moves, then the etching effect of the electrode(s) must be synchronized to such motion in order to leave a desired two dimensional distribution of residual metal on the substrate. The present invention synchronizes variations in the electrode current with the motion of the substrate to remove a desired pattern of metal from the substrate. That is, the electrode current is varied as a function of time, as determined by the particular predetermined etching pattern desired, and by the instantaneous position of the moving substrate.
In a conventional electro-chemical etching process a piece of metal is immersed in an electrolyte bath. A substantially uniform electrical potential is applied to the metal relative to the electrolyte, which is at a different substantially uniform electrical potential (usually ground potential). The electrical potential difference between the metal and the electrolyte, which determines the etching effect, is therefore uniform as well, and hence the electro-chemical effect on the metal is uniform over the entire piece of metal, or large regions thereof. The present invention creates a spatially variable electro-chemical etch effect across the width of the metal surface. Normally, this would be viewed as impossible, as the metal, being an excellent conductor, must have a substantially uniform electrical potential. However, a variable etch effect is possible, as disclosed by the present inventor, because the electrolyte, being a very weak conductor relative to the metal, can support a substantially varying spatial distribution of electrical potential.
By suitably varying the potential of each one of a series of electrodes aligned across, but not in contact with, the metal substrate, the invention is able to cause the electrolyte to have substantially varying electrical potential as a function of position. This causes varying potential differences between the metal and the electrolyte, and hence different etch effects on the metal regions beneath each electrode.
The invention employs a unique insulator configuration to restrict the etch effect to the region beneath the electrode array, thus preventing undesirable spreading of the etching effect. By moving the metal-bearing substrate transversely to the direction in which the electrodes are aligned, and by controlling the potential of each electrode in synchronization with movement of the substrate, the invention is able to achieve any desired two dimensional pattern of removal of metal from the substrate, leaving an arbitrary, non-uniform metal pattern of any desired shape on the substrate.
Some prior art electro-chemical etching processes employ one or more electrodes, each of which extends across the full width of a moving metal substrate which is to be etched. Each such electrode acts on the full width of the substrate. Such electrodes can only etch a uniform pattern. The present invention employs a multiplicity of electrodes aligned across the substrate, transversely to the direction in which the substrate moves. The width of each electrode is much less than the width of the substrate. This allows each electrode to act on substantially different regions across the width of the substrate, by applying different potentials to each region in order to etch a desired, arbitrary pattern.